Energy Confinement Time (τ_E)

τ_E measures how long a plasma holds its heat. Confinement scalings and the required H98 = 1.84 multiplier are expressed against it.

Symbol

τ_E

Meaning

Energy content ÷ heating power

Kronos requirement

H98 = 1.84 over the IPB98(y,2) scaling

Measured at

the G1 confinement testbed

Energy confinement time (τ_E) is the single most important performance number in magnetic fusion: it is the plasma's stored energy divided by the power needed to sustain it — in effect, how long the bottle holds its heat before it leaks out. Longer τ_E means the plasma stays hot with less input, pushing the machine over the Lawson threshold.

Because τ_E cannot be predicted from first principles alone, the field uses empirical scalings — the standard being IPB98(y,2). Performance is then quoted as a multiplier, H98, over that scaling. Kronos MetroVolt requires H98 = 1.84 on a profile basis, which the negative-triangularity confinement is expected to deliver.